Overload And Short-Circuit Protection Device With Improved Breaker Capacity

ABSTRACT

A protective device for an electrical installation, having at least two electrodes between which an elastic arc can electric arc can form, and a device for interrupting ( 6 ) the arc, formed by an assembly of divider plates ( 7 ) and extending between an upstream end ( 6 A) and a downstream end ( 6 B), with an entry region (E) for the arc at the upstream end ( 6 A) thereof. The interrupter device ( 6 ) has an insulation means ( 10 ), formed by caps ( 13 ) that form a partial insulating barrier between the electrodes and the upstream end ( 6 A), the caps ( 13 ) are provided with teeth ( 16 ) housed between two adjacent plates ( 7 ). The invention further relates to overload and short-circuit protection devices.

PRIORITY CLAIM

This patent application is a U.S. National Phase of InternationalApplication No. PCT/FR2005/001888, filed Jul. 21, 2005, which claimspriority to French Patent Application No. 0408095, filed Jul. 21, 2004,the disclosures of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

This invention relates to devices for protecting electrical equipment orinstallations against overvoltages, notably transient overvoltages dueto lightning, overloads or short circuits.

This invention more particularly relates to a device for protecting anelectrical installation against overvoltages, overloads or shortcircuits, including at least two main electrodes between which anelectric arc may form, and a device for breaking the electric arc formedfrom an assembly of splitting plates and extending along the directionof propagation of the electric arc, between an upstream end and adownstream end, and with an entry area for the arc at its upstream end,at which the electric arc penetrates inside the breaker device, thebreaker device including at its upstream end, insulating means againstthe return of the electric arc, structurally designed and arranged so asto allow the electric arc to enter the breaker device while forming anobstacle against the exit of the electric arc, preventing the electricarc from escaping from the inside of the breaker device once theelectric arc is inside the breaker device.

BACKGROUND OF THE INVENTION

There are different categories of devices that may interrupt a current,particularly high intensity current at a conventional frequency (50 Hz).A distinction is made between devices, such as circuit breakers designedto protect an electrical installation against overloads or shortcircuits, and devices used to protect an electrical installation againstovervoltages, such as lightning arresters or surge suppressors.

Such protection devices are usually provided with a current breakingdevice (or a breaking chamber). In the case of circuit breakers, thisbreaker device is intended to provide breaking of short circuitcurrents. In spark gap lightning arresters, the breaker device isintended to provide breaking of follow currents.

The breaker device is generally formed by a plurality of metal splittingplates mounted in parallel so as to break the electric arc down intosmall elementary arcs so as to increase the arc voltage and to providebreaking of the current. Known breaker devices intrinsically have apredetermined breaking capacity corresponding to the maximum value ofcurrent that they are able to extinguish.

Thus, it is found that when the current intensity values are greaterthan the recommended values for a given breaker device, the electric arcmay escape from the breaker device after having penetrated therein andthen form again outside the breaker device, for example following theshortest path between one of the main electrodes and the end of thesplitting plates.

Such a phenomenon is particularly detrimental to the protection deviceinsofar that its effect is to make the attempt to cut off the currentfail. Further, this phenomenon may occur several times within a fairlyshort period. The electric arc may thus enter the breaker device andthen exit from the breaker device and enter the breaker device onceagain, until the unit is destroyed without having been able to cut offthe follow or short circuit current.

It is known that when higher breaking capacities are required, thesedrawbacks may be overcome by increasing the number of splitting plates,putting several protection devices in series or in parallel, or usingadditional mechanisms for physically breaking the electric arc.Nevertheless, all these solutions have a number of drawbacksparticularly related to their application, which is often difficult, anddue to the fact that they lead to a significant increase in the size ofthe protection devices.

SUMMARY OF THE INVENTION

Consequently, the features provided by the present invention provide asolution to the various drawbacks listed above and propose a new devicefor protecting an electrical installation against overvoltages,overloads or short circuits, with improved current breaking capacity.

Another feature of the present invention proposes a new device forprotecting an electrical installation against overvoltages, overloads orshort circuits, with limited bulkiness.

Another feature of the present invention proposes a new device forprotecting an electrical installation against overvoltages, overloads orshort circuits, with a structure particularly well adapted to the caseof strong intensity currents.

Another feature of the present invention proposes a new device forprotecting an electrical installation against overvoltages, overloads orshort circuits that is particularly easy to manufacture.

The features provided by the present invention are achieved by a devicefor protecting an electrical installation against overvoltages,overloads or short circuits including at least two main electrodesbetween which an electric arc is able to form, and an electric arcbreaker device formed by an assembly of splitting plates and extending,considering the direction of propagation of the electric arc, between anupstream end and a downstream end, and with an entry area for the arc atits upstream end, at which the electric arc penetrates inside thebreaker device, the breaker device including at its upstream end,insulating means against the return of the electric arc, structurallydesigned and arranged so as to allow the electric arc to enter thebreaker device while forming an obstacle against the exit of theelectric arc, so as to prevent the electric arc from escaping from theinside of the breaker device once the electric arc is inside the breakerdevice, wherein the insulating means consist of caps arranged so as toform a partial insulating barrier between the electrodes and theupstream end, the caps having teeth positioned at a distance from eachother and adapted to fit between two consecutive splitting plates.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become moreapparent after reading the following description made with reference tothe figures, given as purely illustrative and non-limiting, wherein:

FIG. 1 is a sectional view of one exemplary embodiment of an overvoltageprotection device according to the present invention;

FIG. 2 is a side view of a first exemplary embodiment of a breakerdevice according to the present invention;

FIG. 3 is a front view of the breaker device of FIG. 2;

FIG. 4 is a top view of the breaker device of FIG. 2;

FIG. 5 is a front view of another exemplary embodiment of a breakerdevice for the protection device according to the present invention;

FIG. 6 is a side view of another exemplary embodiment of a breakerdevice for the protection device according to the present invention; and

FIG. 7 is a side view of another exemplary embodiment of a breakerdevice for the protection device according to the present invention.

DESCRIPTION OF THE INVENTION

The device according to the present invention for protecting anelectrical installation against overvoltages, overloads or shortcircuits, is designed to protect an electrical piece of equipment orinstallation. The expression “electrical installation” refers to anytype of apparatus or network subject to voltage perturbations, notablytransient overvoltages due to lightning or even overloads, notablyoverload or short circuit currents. Such devices may consist of sparkgap lightning arresters or surge suppressors provided with a followcurrent breaking device or circuit breakers fitted with a short circuitcurrent breaking device.

In this description, we are more particularly interested in a spark gaptype lightning arrester type device for protection against overvoltages,but the invention obviously applies to circuit breakers.

FIG. 1 illustrates a protection device 1 according to the presentinvention, advantageously formed by a spark gap lightning arrester. Theprotection device 1 comprises at least a first and second electrode 2, 3that may form the two main electrodes of the spark gap lightningarrester, within an insulating casing 20, as illustrated in FIG. 1.These two electrodes 2, 3 are held at a distance from each other andseparated by a lamella 4 in a dielectric material which may improve andbetter control striking of an electric arc between the electrodes 2, 3.This so-called upstream end part of the device is the area for strikingthe electric arc 5.

In the case of a circuit breaker, the electrodes are formed by twocontacts, for example, a fixed contact and a mobile contact, held inphysical contact with each other so as to provide the electricalconnection. In this case, the electric arc is formed between bothcontacts when the mobile contact separates from the fixed contact toprovide electrical disconnection.

According to the present invention and as illustrated in FIG. 1, theprotection device 1 includes a device 6 for breaking the electric arc 5.

In a particularly advantageous way, the breaker device 6 is formed by anassembly of splitting plates 7 made of electrically conducting material,for example, in metal, positioned in parallel and at a distance fromeach other. The splitting plates 7 are advantageously kept at a distancefrom each other by supporting strips 8 made of an electricallyinsulating material.

According to the present invention, the breaker device 6 extends,considering the direction of propagation F of the electric arc 5,between an upstream end 6A and a downstream end 6B. As shown in FIGS.3-5, the breaker device 6 has at its upstream end 6A, an entry area forthe electric arc E at which the electric arc 5 penetrates inside thebreaker device 6. Thus, before penetrating into the breaker device 6,the electric arc 5 propagates along the direction of propagation Fwithin a divergent space 9 extending between the striking area of theelectric arc and the breaker device 6. The divergent space 9 isadvantageously delimited by electrodes 2, 3, and preferably filled withair.

According to one essential feature of the present invention, the breakerdevice 6 includes at its upstream end 6A, insulating means 10 againstthe return of the electric arc 5.

These insulating means 10 are structurally designed and arranged so asto allow the electric arc 5 to enter the breaker device 6 while formingan obstacle against the exit of the electric arc 5, in order to preventthe electric arc 5 from escaping from the breaker device 6 once theelectric arc is inside the breaker device.

The insulating means 6 are adapted to prevent the electric arc 5 fromreturning backwards along a direction opposite to its normal directionof propagation F, in such a way that once the electric arc 5 has beenbroken down into a plurality of elementary arcs within the breakerdevice 6, the electric arc may no longer form again outside the breakerdevice 6, notably in the divergent space 9.

Therefore, the non-return insulating means 10 operate as a ground andare built and positioned relative to the splitting plates 7 on the onehand and to the electrodes 2, 3, on the other hand, so as tosignificantly reduce the likelihood that the electric arc 5 escapes fromthe breaker device 6. Therefore, the design of the protection device 1according to the present invention may significantly improve its shortcircuit current breaking capacity.

The insulating means 10 according to the present invention must providean answer to a new problem which is that of letting the electric arc 5penetrate into the inside of the protection device 6 while limiting thelikelihood that the electric arc escapes and forms again outside thebreaker device 6.

Advantageously, the insulating means 10 are arranged so as to form apartial insulating barrier between the electrodes 2, 3 and the upstreamend 6A of the breaker device 6. The expression “partial insulatingbarrier” refers not only to physical barriers made of electricallyinsulating material, but also to not necessarily physical barriers whichmay be electrically insulating barriers, capable of preventing theformation of an electric arc between the electrodes 2, 3 and theupstream end 6A of the breaker device 6.

Advantageously, the splitting plates 7 extend along the direction ofpropagation F of the electric arc 5, between a front end 7A and a distalend 7B. The front end 7A and the distal end 7B are located atsubstantially the same level as the upstream end 6A and the downstreamend 6B of the breaker device 6. In a particularly advantageous way, thesplitting plates 7 are each provided with a notch 11, at least partiallyseparating each splitting plate 7 into two separate branches 7C, 7D.Thus, when the splitting plates 7 are assembled so as to form thebreaker device 6, the notches 11 form a groove 12, the shape of which,for example a V-shape, is specifically designed to attract the electricarc 5 towards the inside of the breaker device 6. In this way, the entryarea E for the electric arc 5 substantially coincides with the groove12.

According to a first exemplary embodiment of the present invention, theinsulating means 10 are arranged so as to at least partially physicallyclose off the upstream end 6A of the breaker device 6, thus forming aphysical insulating barrier between the electrodes 2, 3 and the upstreamend 6A of the breaker device 6.

Even more preferably, the insulating means 10 are arranged so as toentirely cover the upstream end 6A of the breaker device located aroundthe entry area E for the electric arc 5, for example, on either side ofit. The insulating means 10 may be positioned on either side of thegroove 12, as illustrated in FIG. 3, so as to cover the front end 7A ofthe branches 7C, 7D of the splitting plates 7.

According to a another exemplary embodiment of the present invention,the insulating means 10 may be formed from one or several rigid strips(not shown), for example, positioned on either side of the groove 12 soas to cover the front end 7A of the splitting plates 7. The rigid stripsthen preferably extend along a plane approximately perpendicular to thedirection of propagation F of the electric arc 5, and coplanar with theplane formed by the front ends 7A of the splitting plates 7.

The rigid strips may advantageously be perforated with a plurality oforifices so as to provide air flow between the divergent space 9 and thebreaker device 6.

Preferably, the rigid strips, through one of their faces, come intocontact with the front ends 7A of the splitting plates 7, and preferablybear on them in a sealed manner.

Even more preferably, the insulating means 10 are formed by caps 13arranged so as to form a partial insulating barrier between theelectrodes 2, 3 and the upstream end 6A positioned on either side of thegroove 12 and designed in such a way that, in their functional position,they will also cover the front end 7A of one or several splitting plates7.

Advantageously, the caps 13 are arranged so as to entirely cover theupstream end 6A of the breaker device 6 located around the entry area Efor the arc.

As illustrated in FIGS. 3 and 4, the caps 13 are preferably formed by asubstantially elongated strip 14, designed to cover the front end 7A ofseveral splitting plates 7, and from which a lip 15 is arranged andoriented such that when the cap 13 is in its functional position, thelip 15 will naturally cover the upper edge 12A of the groove 12.

Preferably, the edge 15 of the cap 13 is adapted to substantiallypenetrate inside the groove 12 when the cap 13 is in its functionalposition (FIG. 3).

Even more preferably, and as illustrated in FIG. 3, the cap 13 has asubstantially U-shaped section so as to cover the end of the splittingplates 7, notably of branches 7C, 7D, approximately conforming to theshape of the branches 7C, 7D.

According to one exemplary embodiment illustrated in FIG. 2, the caps 15include teeth 16 positioned at a distance from each other, preferably atregular intervals, and adapted to fit in between two consecutivesplitting plates 7 when the cap 13 is in its functional position. Withthe teeth 16, it is possible to prevent the splitting plates 7 at theirfront ends 7A from deforming and notably moving closer to each other,while improving the insulation properties of the caps 13.

According to one exemplary embodiment of the present invention (notshown in the figures), the insulating means 10 are advantageously madefrom the same material as the casing 20 of the protection device 1, thecasing 20 including the main electrodes 2, 3 on the one hand and thebreaker device 6 on the other hand.

In this case, the shape of the inner surface of the casing 20 isadapted, for example, at the time when the casing 20 is moulded, toexhibit structures in relief capable of forming the insulating means 10.

The insulating means 10 and/or the casing 20 may advantageously be madefrom a rigid material able to withstand the arc temperature, forexample, injected plastic with good temperature resistance, and evenmore preferably an epoxy resin or ceramic.

According to another exemplary embodiment of the present inventionillustrated in FIG. 5, the insulating means 10 are advantageously formedby one or several preferably flexible and adhesive strips 17. Asillustrated in FIG. 5, the strips 17 advantageously cover the front ends7A of the branches 7C, 7D of the splitting plates 7, thus forming caps,similar to the exemplary embodiments described above.

Advantageously, the strips 17 are made in a high-temperature-resistantinsulating material, and notably resistant to the temperature of thearc. Preferably, the strips 17 are made from fiberglass, coated on oneof its faces with a thermosetting type silicone adhesive so as toprovide excellent thermal and mechanical strength.

In a particularly advantageous way, the sticky portion of the strips 17will conform to the upstream end 6A of the breaker device 6, so as tofix the ribbons 17 onto the latter end.

According to another exemplary embodiment of the present inventionillustrated in FIGS. 6 and 7, the insulating means 10 do not form aphysical barrier between the electrodes 2, 3 and the upstream end 6A ofthe breaker device 6, but the insulating means 10 form an immaterialelectrically insulating barrier instead.

According to a first exemplary embodiment illustrated in FIG. 6, theinsulating means 10 are advantageously formed by an electricallyinsulating coating 18 deposited over substantially the entire surface ofthe terminal portion 7E, located towards the front end 7A of one orseveral splitting plates 7. The coating 18 is advantageously positionedso as to cover the terminal portion 7E. The coating 18 may notablyincrease the distance to be travelled by the electric arc to form againoutside the breaker device 6. Therefore, the presence of the coating 18may reduce the likelihood that the electric arc may form again betweenboth main electrodes 2, 3 outside the breaker device 6.

According to another exemplary embodiment of the present inventionillustrated in FIG. 7, the insulating means 10 are formed by insulatingplates 19 positioned on either side of the groove 12 and insertedbetween two successive splitting plates 17 so as to extend towards theoutside of the breaker device 6, beyond the front end 7A of thesplitting plates 7. The insulating plates 19 may also prevent theelectric arc from escaping outside the breaker device 6 by increasingthe distance that the electric arc needs to travel to form again outsidethe breaker device 6, between the main electrodes 2, 3.

According to another more preferred exemplary embodiment of the presentinvention, the breaker device 6 includes, at its downstream end 6B, aninsulating screen 30 positioned so as to at least partially cover thedownstream end 6B of the breaker device 6 so as to prevent the electricarc 5 from escaping from the breaker device 6 after the electric arc haspassed through the breaker device, for example once (FIG. 1).

In this preferred exemplary embodiment, the insulating means 10 have acrucial role in that, after passing through the breaker device 6 alongthe direction of propagation F, the electric arc 5 “rebounds” on theinsulating screen 30 and then continues in a direction substantiallyopposite the direction of propagation F, towards the upstream end 6A ofthe breaker device 6. In such a configuration, the applicant hasobserved that the electric arc 5 preferably returns along the branches7C, 7D of the splitting plates 7 and much more rarely to the centralportion 12B of the groove 12.

Consequently, in this exemplary embodiment, the insulating barrierformed by the insulating means 10 may notably reduce the likelihood thatthe electric arc escapes at the upstream end 6A of the breaker device 6,thereby preventing the electric arc 5 from forming again between themain electrodes 2, 3.

Operation of the protection device 1 according to the invention will nowbe described, with reference to FIGS. 1-7.

During operation, when an overvoltage exceeding a predeterminedthreshold value occurs, notably as a result of a lightning strike, anelectric arc 5 is established between one of the two main electrodes 2,3 allowing the lightning current to flow to ground. This electric arc 5then moves up to the breaker device 6 into which the electric arcpenetrates at the entry area E, located in approximately the same planeas the groove 12. The electric arc 5 is then broken down into aplurality of elementary arcs so as to increase the arc voltage of thecurrent above the mains voltage and limit the intensity of the currentdrained by the protection device. The elementary electric arcs movetowards the downstream end 6B of the breaker device 6 until they reachthe insulating screen 30. A “rebound” phenomenon then occurs and theelementary electric arcs leave in the direction opposite to the initialdirection of propagation F of the electric arc 5, towards the downstreamend 6A of the breaker device 6. According to the most likely operatingmode, the elementary electric arcs move towards the branches 7C, 7D andmore specifically along these branches as far as their front end 7A.

They are then trapped by the insulating means 10 which prevent theelectric arc 5 from forming again outside the breaker device 6.

Therefore, the protection device 1 according to the present inventionhas a better short circuit current or follow current breaking capacitythan the current breaking capacity for devices according to the priorart, while limiting the likelihood that the electric arc, once insidethe breaker device and broken down into a plurality of elementary arcs,escapes from the breaker device to form again outside the breaker devicebetween the main electrodes.

By the presence of the insulating means 10, the protection deviceaccording to the present invention has a current-breaking powermultiplied by at least two as compared with devices from the prior art.

The invention finds one aspect of its industrial application in thedesign, the manufacturing and the use of protection devices againstovervoltages, overloads, or short circuits.

1. A device for protecting an electrical installation againstovervoltages, overloads or short circuits, comprising: at least two mainelectrodes between which an electric arc is able to form; an electricarc breaker device formed by an assembly of splitting plates andextending, considering the direction of propagation of the electric arc,between an upstream end and an downstream end, and with an entry areafor the arc at its upstream end, at which the electric arc penetratesinside the breaker device, wherein the breaker device includes at theupstream end, insulating means against the return of the electric arc,structurally designed and arranged to allow the electric arc to enterthe breaker device while forming an obstacle against the exit of theelectric arc, to prevent the electric arc from escaping from the insideof the breaker device once the electric arc is inside the breakerdevice, the insulating means consist of caps arranged to form a partialinsulating barrier between the electrodes and the upstream end, the capshaving teeth (16) positioned at a distance from each other and adaptedto fit in between two consecutive splitting plates.
 2. The device ofclaim 1, wherein the caps are arranged to entirely cover the upstreamend of the breaker device located around the entry area for the arc. 3.The device of claim 1, wherein the assembly of splitting plates extendsalong the direction of propagation of the electric arc, between a frontend and a distal end, the splitting plates having a notch to form, oncethey are assembled, a groove arranged in order to attract the electricarc such that the entry area for the arc substantially coincides withthe groove.
 4. The device of claim 3, wherein the caps are positioned oneither side of the groove and designed such a that, in their functionalposition, the caps cover the front end of one or several splittingplates.
 5. The device of claim 4, wherein the caps are formed by asubstantially elongated strip, intended to cover the front end ofseveral splitting plates, and from which an edge extends, arranged suchthat when the cap is in the functional position, the edge naturallycovers the upper edge of the groove.
 6. The device of claim 5, whereinthe edge of the cap is adapted to penetrate inside the groove when thecap is in the functional position.
 7. The device of claim 3 wherein thecaps have a substantially U-shaped section.
 8. The device of claim 1,further comprising: a casing in an electrically insulating material,within which the main electrodes and the breaker device are mounted, andin that the insulating means are made of the same material as thecasing.
 9. The device of claim 8, wherein the insulating means and thecasing are made by moulding from an injected plastic, epoxy resin orceramic type material.
 10. The device of claim 1, wherein the breakerdevice includes an insulating screen at the downstream end positioned toat least partially cover the downstream end of the breaker device toprevent the electric arc from escaping from the breaker device after theelectric arc has passed through the breaker device.
 11. The device ofclaim 2, wherein the assembly of splitting plates extends along thedirection of propagation of the electric arc, between a front end and adistal end, the splitting plates having a notch to form, once they areassembled, a groove arranged in order to attract the electric arc suchthat the entry area for the arc substantially coincides with the groove.12. The device of claim 4, wherein the caps have a substantiallyU-shaped section.
 13. The device of claim 5, wherein the caps have asubstantially U-shaped section.
 14. The device of claim 6, wherein thecaps have a substantially U-shaped section.